Rotary kiln



June 1l, 1940.

L. J. MUELLER 2,204,145

ROTARY KILN Filed sept. so, 195s D :inventor: @im/wy Me/v (Ittornegs Psa-nad Junen 11, 1940 VUNITED sTATEs PATENT OFFICE TheStandardLimeandS Baltimore. Md., a corporation of Maryland Application September 30, 1938, Serial No. 232,662

5 Claims.

This .invention pertains to rotary kilns, and has for its main object the recovery of heat from the gases discharged from the kiln. 'I'his heat is now commonly lost, or is sometimes used in waste heat boilers'or for drying processes. Most of the recovery processes heretofore utilized have necessitated the employment of neans exteriorly of the kiln; whereas the present invention recovers the heat from the exhaust gases within the kiln itself or an integralportion thereof.

In the embodiment of the invention herein shown and described, preheating chamber is employed as a part of the kiln. This chamber likewise acts as a reservoir forthe material to be treated in the kiln, and the exhaust gases from the kiln are drawn through'such reservoir and the material therein by induced'suction. Means is also provided in connection with said chamber and the adjacent portion of the kiln to ensure adequate and' definite feeding of the material from the preheating chamber into the kiln, the amount of feed varying with the speed of the kiln and certain other factors hereinafter mentioned.

Broadly stated, the invention comprises a rotary kiln in communication with a feeding and heat exchange chamber through a series f tubes or pipes extending from said chamber into the kiln, and means for exhausing the gases from the kiln through said pipes and feed chamber, whereby the heat of the gases is absorbed by the material to be treated while it is within the tubes and the feeding chamber.

Another object of the invention is to provide means to preclude the material from being drawn outwardly from the feeding chamber by the exhausting means. A further object is to provide means for periodically feeding an additional amount of material to be treated to the feeding chamber to maintain the same in its fully charged condition, 'said means being automatically controlled through the rotation of the kiln and so constructed and operated as to prevent the escape of gases from the chamber or the indrawing of air therethrough except when the automatic mechanism is actuated to admit additional ma-C Fig. 2 is a vertical sectional view taken on the line II-II of Fig. 1, with a portion of the wall of the feeding chamber and other elements broken away to more clearly show the structure.

In the drawing, It denotes a portion of the vrotary kiln whic ;v as usual, is slightly inclined 'feeding chamber is provided. In the structure shown in Fig. 1, said chamberisdeilned by the walls-(I, t2 and I3, the wall II extending outwardlyjfrom the' body of the kiln. I0. Extending inwardly into the feed end of the kiln is a series of cylindrical tubes I4 which are open at each end, the innermost ends being secured by welding or otherwise in openings formed in the wall II. These tubes are shown as having the same inclination as the kiln III and are in free communication with the interior of the preheating and feeding chamber. While this chamber is ,shown In the drawing as being of `a diameter larger than that of the kiln III, its diameter may vary and, for instance, be the same as that of the kiln Il. This being a mere matter of proportion, it is not deemed necessary to illustrate the same.

Extending outwardly from the wall I3, in line with the axis thereof, is a nozzle or cylindrical jmember I5 which extends into a similar member I6 interconnected with the housing I'I of an exhaust fan. A suitable packing, as 20, will be interposed between Ithese members to prevent the infiltration of outside air. vA screen I8 extending transversely of 'the combined preheating and feeding chamber precludes the indrawing of the material into the.fan from said feed chamber. The mesh of the screen is determined by the si'ze of the material undergoing treatment.

In order to introduce material such as limestone, if that be the material to be treated, into the preheating and feeding chamber, the annular wall I2 is provided with an opening I9. (see more particularly Fig. 2) which is designed to be normally closed by a gate or valve 2l secured to a shaft 22, one end whereof extends outwardly ofthe feed chamber and is fashioned into a crank..

arm 23. -An adjustable weight (or weights) 2 4 is mounted and secured upon the crank arm and tends to hold the gate 2i closed while said gate is traveling with the chamber through the upper l portion-ofits cycle.

Secured to a tlxed element of the kiln-support-v ing structure 25 is a cam 26 which stands in the path of the crank arm and contacts said arm as p the kiln is rotating. When the parts are in the hopper or spout-like element 21 is positioned to one side of the wall l2,lthe lower end, of the hopper being contoured upon'the same radius as that of said wall. Assuming that the crank arm has passed off of the cam surface, the counterweight will, as above mentioned', close the valve. As the kiln continues to rotate, the angle of repose ofthe material Within the kiln will change and the material will pile up against the inner face of the gate or valve and thus hold it closed until the parts come to a position where the inner face of the valve is relieved of any pressure from the material within the chamber. This permits the cam surface 26 vto function and open the valve to introduce another portion of the charge. As the kiln and the combined preheating and feeding chamber are rotated, the material will pass into the tubes il and will eventually work outwardly through their unobstructed ends onto the inner surface of the kiln il). Not only does the arrangement ensure adequate and proper feeding of the material, but the material is, in a sense, showered from the tubes transversely of the kiln into direct contact with the hot gases being drawn therefrom. As will be appreciated and seen upon reference to Fig. l, the material falls Aacross the mouths of the tubes through which the hot gases are drawn so that the heat is abstracted in a most eficient manner. Moreover, this curtain of falling material, as it may be termed, falls past the discharge ends of all of the tubes H other than the uppermost in the orbit so that the gas cannot short circuit through the apparatus. Ihe path of the gases is indicated by the arrows in Fig. 1.A Such heated gases will contact the material thus showered and thence pass through the tubes and the material therein, into the preheating and feeding chamber and through the material therein, then through the screen i8 and through the nozzle i5 and, ultimately, into the intake housing il of th exhaust fan.

The rate of feed of the material into the kiln fother factor is the number of the tubes iii as well as their length and diameter.

Qi-the diameter of the tubes and the smaller the The smaller .fnumber, the less rapid will be .the feed. On the other hand, if the number be increased and the diameter enlarged, greater feed will obtain with the same rotative speed of the kiln.

The depth of the material in the feed chamber between the intake of the feed tubes and the screen I8 is a factor to be considered in the absorption of the heat from the gases which pass through the material being fed to the retort. This depth is also limited by the characteristic of the material; that is, material of small void volume will require less thickness of material between the screen and the pipes to absorb the heat than one with a large void volume. The material in the feed chamber must, of course, be

maintained at such depth that the mouths at the as is indicated in the drawing. Y

Actual use of a kiln constructed as above described has proved its success, and one is able to regulate the feed and reduce the temperature of the gas to a point where it is profitable to install `a motor-driven exhaust fan to suck the gases from the kiln through the resistance of the stone or other material in the combined preheating a-nd feeding chamber and the feeding tubes.

By employing a suction fan connected to the head end of the kiln, one is enabled to speed the operation. It is conceivable, of course, that the feeding chamber defined by the walls ii, i2 and 93, together -with the tubes I4, may be utilized as a feeding means without the necessity of employing the suction fan. In other words, with certain materials it may become advisable to operate the kiln in the absence of a fan and t merely vent the feeding chamber.

While I have shown and described the feed tubes as being cylindrical, they may be polygonal in cross section, and this form may have the advantage of agitating the material to a greater degree as the gas passes through the material in the tubes. One such tube is indicated at Ma.

What is claimed is:

l. In a rotary kiln for the treatment of dry material, a kiln section or chamber for receiving the material to be treated within the kiln, said section being enlarged circumferentially with reference to the diameter of the kiln; a plurality of tubular members extending from the forward portion of said chamber directly into said kiln, said tubular members being substantially of the same length throughout the series and likewise of the same internal diameter throughout and. free from obstruction from the intake to the discharge end thereof; a foraminous surface or partition located adjacent the opposite end of the enlarged chamber, said chamber being in communication with the offtake of the kiln; means for introducing material into said enlarged chamber and maintaining it substantially full of such material; and means for rotating the kiln.

2. A structure as set forth in claim l, wherein the enlarged chamber is provided at its periphery with at least one opening in communication with the interior of said chamber; a valve normally closing said opening; a fixed hopper located in line with said opening and normally closed by the circumferential Wall of the chamber; and means for periodically opening the valve when the opening in the enlarged chamber comes into registry with the discharge opening in the hopper. whereby material will pass from said hopper into the enlarged chamber and said chamber will be kept substantially full and short-circuiting of the gases passing through the kiln tothe offtake will be precluded.

3. In a rotary kiln, the combination of a kiln body cylindrical in cross section; a chamber located at the head end of said kiln, said chamber being of a diameter in excess of the diameter of the kiln proper and in communication with the ottake of the kiln; a series of tubular members extending into the kiln from said chamber and terminating within the kiln` proper, said tubular members being of the same diameter and length and free of obstruction throughout and aording the sole communication between the enlarged chamber and the interior of. the kiln; a. foraminous element located Within the enlarged chamber for preventing passage of material therefrom other than the gases and dust which may inhere from the operation of the kiln; and means for introducing -material to be treated into said enlarged chamber and maintaining it substantially full at all times, said means being so related to the chamber as to prevent egress of gases therethrough when the parts of said means are in charging position.

4. In a rotary kiln for the treatment of dry material, the combination of an inclined kiln body; a circumferentially enlarged feed chamber located at the intake end of said body; a series of tubular members extending outwardly from said chamber directly into the adjacent portion of the kiln and in free communication at their intake ends with the feed chamber, said tubular members vbeing unobstructed from the intake to the discharge end thereof; a screen surface located within the feed chamber adjacentl an offtake of the gases therefrom; and means for maintaining said feed chamber substantially full of material to be treated, whereby the material will be fed from said chamber simultaneouslyV into and through all of said tubular members aforesaid and thence from the tubular members directly into the body proper of the kiln.

5. In a rotary kiln for the treatment of dry material, a kiln chamber or section for receiving the material to be treated within the kiln, said section being enlarged circumferentially with reference to the diameter of the kiln; a plurality of tubular members extending from the forwardl portion of said chamber directly in to said kiln, each of said tubular members being of` substantially the same internal diameter throughout and free from obstruction from the i-ntake to the discharge end thereof; a foraminous surface or partition located adjacent the opposite end of the enlarged chamber, said chamber being in communication with the offtake of the kiln; means for introducing material into said enlarged chamber and maintaining it substantially Afull of the material to be treated, said means comprising a valve normally closing an opening formed in the periphery of the enlarged chamber, a fixed hopper located in line with said opening and normally closed by the circumferential Wall of the chamber, and means for periodically opening the valve when the opening in the en larged chamber cornes into registry with the discharge opening in the hopper, whereby material is passed from said hopper into the enlarged chamber; and means for rotating the kiln.

LOUIS J. MUELLER. 

